Mechanisms known as gerotors, which are fluid pressure devices that form expansable and contractable chambers, are well known. One particular type of gerotor device that has found commercial acceptance is formed with a generally cylindrical shaped casing which is annular and has a number of internal teeth. An external tooth star member, or gear, having at least one fewer tooth than the casing, or ring member, has its teeth in meshing engagement with teeth of the ring member. The star gear partakes of a hypocycloidal movement so that the axis of the star gear travels in an orbit about the axis of the ring member.
Various versions of gerotor mechanisms which use an orbiting star gear, of the type that is the subject of the present invention, are shown in U.S. Pat. No. 1,682,563, issued Aug. 28, 1928 to Myron F. Hill; U.S. Pat. No. 3,283,723, which issued Nov. 8, 1976 and which was assigned on its face to the Germane Corporation; U.S. Pat. No. Re. 25,291, issued Dec. 4, 1962 which was assigned on its face to the Germane Corporation; and in the following U.S. Patents which were assigned on their face to the Chr-Lynn Company; U.S. Pat. No. 3,270,683, issued Sept. 8, 1966, U.S. Pat. No. 3,272,142, issued Sept. 13, 1966, and U.S. Pat. No. 3,514,234 issued May 26, 1970.
In the past, the accurate machining and checking of the profile of a star gear has proven to be troublesome. In particular, it has proven to be especially difficult to check with high accuracy the profile of a star gear with standard gear checking equipment. The present invention is directed to a machine which traces the profile of a star gear in a highly accurate manner and which, thus, may be used either to test the profile of a completed star gear for accuracy or, alternatively, to generate a very precisely formed star gear from a cylindrical workpiece.